On Fri, 18 Sep 2020, Patrick Palka wrote: > This fixes a division by zero in the selection-sampling std::__search
Whoops, this line say std::__sample, not std::__search. > overload when the input range is empty (and hence __unsampled_sz is 0). > > Tested on x86_64-pc-linux-gnu. > > libstdc++-v3/ChangeLog: > > * include/bits/stl_algo.h (__sample): Exit early when the > input range is empty. > * testsuite/25_algorithms/sample/3.cc: New test. > --- > libstdc++-v3/include/bits/stl_algo.h | 3 ++ > .../testsuite/25_algorithms/sample/3.cc | 50 +++++++++++++++++++ > 2 files changed, 53 insertions(+) > create mode 100644 libstdc++-v3/testsuite/25_algorithms/sample/3.cc > > diff --git a/libstdc++-v3/include/bits/stl_algo.h > b/libstdc++-v3/include/bits/stl_algo.h > index a0b96c61798..2478b5857c1 100644 > --- a/libstdc++-v3/include/bits/stl_algo.h > +++ b/libstdc++-v3/include/bits/stl_algo.h > @@ -5775,6 +5775,9 @@ _GLIBCXX_BEGIN_NAMESPACE_ALGO > using _Gen = remove_reference_t<_UniformRandomBitGenerator>; > using __uc_type = common_type_t<typename _Gen::result_type, _USize>; > > + if (__first == __last) > + return __out; > + > __distrib_type __d{}; > _Size __unsampled_sz = std::distance(__first, __last); > __n = std::min(__n, __unsampled_sz); > diff --git a/libstdc++-v3/testsuite/25_algorithms/sample/3.cc > b/libstdc++-v3/testsuite/25_algorithms/sample/3.cc > new file mode 100644 > index 00000000000..e89c40e27ee > --- /dev/null > +++ b/libstdc++-v3/testsuite/25_algorithms/sample/3.cc > @@ -0,0 +1,50 @@ > +// Copyright (C) 2020 Free Software Foundation, Inc. > +// > +// This file is part of the GNU ISO C++ Library. This library is free > +// software; you can redistribute it and/or modify it under the > +// terms of the GNU General Public License as published by the > +// Free Software Foundation; either version 3, or (at your option) > +// any later version. > + > +// This library is distributed in the hope that it will be useful, > +// but WITHOUT ANY WARRANTY; without even the implied warranty of > +// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the > +// GNU General Public License for more details. > + > +// You should have received a copy of the GNU General Public License along > +// with this library; see the file COPYING3. If not see > +// <http://www.gnu.org/licenses/>. > + > +// { dg-options "-std=gnu++17" } > +// { dg-do run { target c++17 } } > +// { dg-require-cstdint "" } > + > +#include <algorithm> > +#include <random> > +#include <testsuite_hooks.h> > +#include <testsuite_iterators.h> > + > +std::mt19937 rng; > + > +using std::sample; > +using __gnu_test::test_container; > +using __gnu_test::output_iterator_wrapper; > +using __gnu_test::forward_iterator_wrapper; > + > +void > +test01() > +{ > + const int in = 0; > + test_container<const int, forward_iterator_wrapper> pop(&in, &in); > + int out; > + test_container<int, output_iterator_wrapper> samp(&out, &out + 1); > + > + auto it = sample(pop.begin(), pop.end(), samp.begin(), 1, rng); > + VERIFY( it.ptr == &out ); > +} > + > +int > +main() > +{ > + test01(); > +} > -- > 2.28.0.497.g54e85e7af1 > >